Electric retrieval system



April 21, 1970 E. L. HOOVER 3,508,001

ELECTRIC RETRIEVAL SYSTEM Filed June 24, 1966 5 Sheets-Sheet 1 BANKSCONTROL gg j f OF UNIT |5 (CONTACTS no 22 1 LESSON SOURCES P 1 CONNECTOR23 23 ERROR 24 I SENSING MODULE S TC ADAPTER ASSEMBLY MODULE Fig. 1

F BANKS POWER OF I SOURCE l5 CONTACTS CONTROL UNIT 22 32 s 23 LESSONCONNECTOR 1 23 SOURCES 2 ADAPTER MODULE SWITCH ASSEMBLY INVENTOR. F18.

EDWIN L. HOOVER BY I L LA ATTORNEYS A ril 21, 1979 i-z. L. HOOVERELECTRIC RETRIEVAL SYSTEM Filed June 24, 1966 5 Sheets-Sheet 2 N o mINVENTOR.

EDWIN L. HOOVER 00 000 00 0O O0 O0 00 0O 00 on 0 0 00 0o no ou oo oo co00 00 0000 on 000 coco coo 0 000 00 QONQOOQ 0 m 00 00/ oo 00 no 00QOOOOO/AO O0 O0 000 mN w 3 m m m w Q i J n n i i @N .i 3 n 2 n wi mi wiwi \BN 3 n J 3 3 3 i: w wmm M wk m w 3 n w m m n m R3 3 3 w E w l l hhwm 1 A ril 21, 1970 E. L. HOOVER 3,508,001

ELECTRIC RETRIEVAL SYSTEM Filed June 24, 1966 5 Sheets-Sheet 5 R k 5 mmJW 0 \oh mm mm H d 8 K v A NM mL 0 om mm g pkwfi mm mm m wm L w w k NEmm D w mm 91 E mm 8 mm P T oO 0 I b h m A x 06 w mm 8 RR m? vm H mm mmmm m mm N N m9 1 6 Q N m mm mm) M E .3. N 09 E 3 02 3: 2i wy ow: N. 02 5me n m v 1 w: 9 2 5 mo. $1: 91 1%. mm 2 Q 9 o I Q 1 m m u 0 m9 1 8 fl 87I N o m9 2. I 5. mm. m

ATTORNEYS April 1979 E. L. HOOVER 3,508,001

ELECTRIC RETRIEVAL SYSTEM Filed June 24, 1966 5 Sheets-Sheet 5 2 3 4 5 67 8 9 IO H INVENTOR. EDWIN L. HOOVER Fig. 6

A YTORNEYIS United States Patent O 3,508,001 ELECTRIC RETRIEVAL SYSTEMEdwin L. Hoover, Lafayette, Ind., assignor to P & H Electronics,Lafayette, Ind., a partnership Filed June 24, 1966, Ser. No. 560,238

Int. Cl. H04r 3/00 U.S. Cl. 179-1 4 Claims ABSTRACT OF THE DISCLOSURE Anelectric system having a group of listening stations for selectingmessages from a remotely positioned plurality of message sources. Foreach listening station there is a bank of contacts arranged in rows andcolumns and connected to the various message sources which are swept bya set of wipers coupled to a loud speaker. The wipers form a part of atwo-motion switching assembly which is controlled by a module connectedto a selector switch at the listening station. Selection of a particularmessage is initiated by operating the selector switch at the listeningstation to furnish two signals to the module which controls the twodirections of motion of the wipers on the bank of contacts. Apparatus isdisclosed wherein the selector switch may be interchangeably replaced byeither a dial switch, which furnishes a train of pulses, or a switchwhich supplies a pair of DC voltages corresponding in amplitude to thecoordinates of the chosen location on the bank of contacts. In the caseof a dial switch the first train of pulses moves the wipers in onedirection while the second train of pulses moves said wipers in theother direction of movement on the bank of contacts. Where a switch isused for supplying DC voltages, said voltages are compared with DCvoltages on a second set of contacts forming a part of said bank ofcontacts until a null condition results between the contact voltages atthe wipers and the DC voltages from the selector switch. The number oflistening stations can be multiplied by simply connecting additionalbanks of contacts and their associated circuitry to the message sources.

This invention relates to an electric message retrieval system whereinan audible message can be selectively actuated and transmitted to alocation remote from the source of said message.

It is an object of this invention to provide such a retrieval system inwhich an individual can from a remote location selectively actuate andreceive an audible message, which will permit such selection from aplurality of messages, which will permit such selection to be quicklyand easily effected, which will permit changes in the selection duringtransmission of the message, which can be actuated by a plurality ofdifferent modes, and which will permit a plurality of individuals toselect and receive the desired messages.

The instant invention is adapted to permit a plurality of individuals atpositions remote from each other to selectively actuate and receivemessages in audible form from a bank of such messages which can belocated at a point remote from each of the individuals. For example, itmay be employed as a teaching aid wherein a plurality of students caneach selectively actuate and receive a ice can remain the sameirrespective of the use made of the invention.

In accordance with the invention, each student location is provided witha control unit. Said unit is provided with switch means for selectivelyactuating the desired lesson and with audio receiving means,conveniently in the form of headphones, for receiving the transmittedlessons. The switch means in the control unit is electrically connectedto an adapter module which, upon selective actuation of the switchmeans, controls the operation of a two-motion switch assembly. Thelessons are connected to contacts in the two-motion switch assembly andthrough said assembly to the headphones at the student location. Thus,selective actuation of the switch means at the student location causesthe adapter module to close the desired contacts in the two-motionswitch assembly to actuate the desired lesson for transmission to thestudent location.

The adapter module and the two-motion switch assembly are connected to apower source for supplying electrical power to the various components ofthe system. Desirably, a plurality of different types of switch meanscan be employed in the control unit and only the adapter module need bechanged in the system in-order to accommodate the use of such dilierenttypes of switch means at the student location.

Other objects and features of the invention will become apparent fromthe more detailed description which follows and from the accompanyingdrawings, in which:

FIG. 1 is a schematic diagram showing a message retrieval systemembodying my invention;

FIG. 2 is a wiring diagram of the student control unit, power supply,and contact banks shown in FIG. 1;

FIG. 3 is a wiring diagram of the adapter module and switching assemblyshown in FIG. 1;

FIG. 4 is a schematic diagram showing a modified embodiment of a messageretrieval system embodying my invention;

FIG. 5 is a wiring diagram of the student control unit, power supply,and contact banks shown in FIG. 4; and

FIG. 6 is a wiring diagram of the adapter module and switching assemblyshown in FIG. 4.

pre-recorded lesson from a bank of such lessons. It may In the systemillustrated in FIGS; 1-3, the student control unit 10 comprising adigital selector switch 11 and headphones 12 is connected through plug Pand socket S to an adapter module 14. Each student module 14 isconnected to a common power source 15 through plug P andsocket S andthrough plug P and socket S to a two-motion switch assembly 16 having aplurality of wipers 17, 18, 19, 20, and 21 selectively engageable withbanks of contacts 22, the contacts in said banks of contacts engageablewith the indexing wipers 17 and 18 also being connected to said powersource. In the illustrated single wire system, each of the lessons 23 isconnected to ground, as at 24, and to one of the contacts in the contactbanks 22. One side of the headphones 12 is connected to ground, and theother side of said headphones is connected by means ofaudio-transmitting wipers 19-21 through certain of the contacts incontact banks 22 to the lessons 23 to thus complete the circuit fromsaid lessons to the headphones upon actuation of the selector switch 11,said lessons having their own power source. Normally, the power source15, switch assemblies 16 and their associated contact banks 22 arelocated at positions remote from the student locations.

As shown in FIG. 2, the contact banks 22 comprise one bank of tencontacts 25 adapted to cooperate with wiper 17 to index wipers 17-21 ina decade direction and one bank of ten contacts 26 adapted to cooperatewith wiper 18 to index wipers 18-21 in a units direction. Said contactbanks also contain ten banks of ten contacts 27 adapted to cooperatewith wiper 19, ten banks of ten contacts 28 adapted to cooperate withwiper 20, and ten 3 banks of ten contacts 29 adapted to cooperate withwiper 21. Each of the contacts 27, 28, and 29 is connected to one of thelessons 23 to thus permit a total of 300 different lessons to beconnected to the system.

As shown, the power supply is connected to ground at 32 to thus groundthe first contact 25 in the bank of contacts 25 and the first contact 26in the bank of contacts 26 by means of line 33. Switch 11 is connectedto ground 32 through lines 34 and 35. Said power supply also supplies,through line 37, a fixed reference voltage to the tenth contact 25 inthe bank of contacts 25 and the tenth contact 26 in the bank of contacts26. In a like manner, said reference voltage is supplied to the controlswitch 11 through line 40. A pair of AC current carrying lines 42 extendfrom the power supply to feed one side of a transformer 44 with lines 46extending from the opposite side of said transformer to the adaptermodule 14. The necessary DC voltage to operate the various solenoids andrelays in the adapter module 14 and switch assembly 16 is supplied tosaid module and assembly from the power supply through line 48.

With the first contact in each of the contact banks 25 and 26 connectedto ground 32 through line 33 and the tenth contact in the banks 25 and26 connected by line 37 to the reference voltage of the power supply, avoltage drop is provided across the contact banks 22. Each of theintervening contacts 25 and 26 is also connected by a line 50 to areference voltage in the power supply. The voltage is graduated betweenlines 33, adjacent lines 50, and line 37 in equal increments so thatthere is an equal potential difference between adjacent contacts 25 andadjacent contacts 26. In a similar manner, the control unit switch 11has ten pairs of contacts 52 and 53. A plurality of impedances 54 arewired in series between the adjacent pairs of contacts 52 and 53 andprovide an equal voltage drop between adjacent pairs of said contacts sothat the incremental voltage drop across the control unit switch 11corresponds to the incremental voltage drop across the contacts 25 and26 in the banks of contacts 22.

To select one of the lessons 23, the student moves switch 56 along thecontrol unit contacts 52 until it closes against the contact 52corresponding to the first digit in the lesson which he desires. He alsomoves switch 58 along contacts 53 until it closes against the contact 53corresponding to the second digit of the lesson which he desires.Conveniently, movement of switches 56 and 58 can be effected by handwheels, control knobs, or the like. Moving switches 56 and 58 into thedesired position momentarily closes control unit switches 59 and/or 60which are connected by line 62 to one side of relay 64 in adapter module14, the opposite side of said relay being connected by line 48 to thepower supply 15.

Energization of relay 64 moves switch blade 66 from contact 67 tocontact 68 to supply DC power through line 70 to contacts 72 and 73 inassembly 16. Blades 74 and 75 closed against contacts 72 and 73 transmitsaid power through line 76 to one side of reset coil 78, the oppositeside of said coil being connected to ground 32 through lines 80 and 35.Actuation of reset coil 78 causes means (not shown) to move wipers 17-21to their home position out of engagement with any of the contacts 25-29in the contact banks 22. With the momentary closing of switches 59and/or 60, capacitor 82 and resistance 84 in the adapter module 14 willcause relay 64 to remain energized for a time suflicient to permit coil78 to return wipers 17-21 to home position. This time delay furtherprevents the switch assembly from being actuated to move wipers 17-21while switches 56 and 58 are being closed against the desired contacts52 and 53 since the wiper movement cannot be effected until relay 64 isdeenergized.

With relay 64 closing blade 66 against contact 68, DC current will alsobe supplied through line 86 and diode 88 to relay 90. This energizesrelay 90 to move switch blade 91 from contact 92 to contact 93 to thusconnect control unit switch 56 through lines 94 and 95 to the errorsensing module 96 of adapter module 14 for transmitting the electricalunbalance of the control unit 11 to module 96, modules 14 and 96 beinginterconnected through plug P and socket S The reference potential inthe contact banks 22 is picked up by wiper 17 engaging one of thecontacts 25 and is transmitted through line 98 to contact 100. Switchblade 101 will have moved from contact 102 to contact upon actuation ofrelay 90 so that the reference potential from wiper 17 is transmittedthrough switch blade 100 and line 103 to module 96.

Since wiper 17 would not be closed against any one of the contacts 25 atthe beginning of the switching operation, it is necessary to provide avoltage unbalance in the home position. This is accomplished by switchblade 104 and its contact 105 in the switch assembly 16 which areconnected through a branch of line 98, switch blade 101 and its contact100, and line 103 to module 96 and through line 47 to the power supply;line 47 providing an unbalance voltage from the power supply. As long asan electrical unbalance exists between wiper 17 or switch blade 104 andthe control unit switch 56, relay 108 in the adapter module 14 will beenergized by action of the error sensing module 96.

As shown in FIG. 3, the module 96, which senses the unbalance betweenthe switches in the student control unit 10 and the switch assembly 16and contact bank 25, contains an NPN transistor 110 having its emitterconnected by line 111 to the emitter of a PNP transmitter 112, the line111 being connected to line 103. A pair of the lines 46 leading from thetransformer 44 are connected to the module 96 and supply a positivepotential to the collector of transistor 110 through diode 114 andfilter capacitor 115 and a negative potential to the collector oftransistor 112 through diode 116 and filter capacitor 117. The bases ofthe transistors are interconnected by line 118, and line 95 is connectedto line 118 so that the unbalanced voltage is applied to the module atpoint A from line 95 and at point B from line 103. The voltage on line95 (with switch blade 91 closed against contact 93) is a function of thepositioning of the switch 56 along contacts 52, and the voltage at pointB is a function of the voltage on wiper 17 or switch blade 104. Whenpoint A is positive with respect to point B, transistor 110 will berendered conductive to permit current to flow outwardly through line 103to relay 108 and return through line 120 to the center tap oftransformer 44 to energize relay 108 for keeping its switch 122 closedso that wiper 17 will continue to advance along contacts 25 in thecontact banks 22 until a balanced condition is reached. Conversely, whenpoint A is negative with respect to point B, transistor 112 will beconductive to render relay 108 energized until wiper 17 advances alongcontacts 25 to reach a balanced condition. Desirably, current limitingresistors 124 are interposed between the collectors of transistors 110and 112 and the take-off of transformer 44, and capacitors 125 areinterposed between emitters of said transistors and the transformer toprevent chatter of relay 108 as wiper 17 moves from one contact 25 toanother.

DC current from line 48 is free to flow to switch 122 by reason of relay64 becoming de-energized after student selection and discharge ofcapacitor 82 so that said current can flow through switch blade 66 andcontact 17-21 to automatically step in a decade direction in contactbanks 22 by means not shown. In such advancement, wiper 17 steps fromone contact 25 to another and wipers 18-21 will step along the rows ofcontacts 26-29 in a left-right direction. The wiper 17 will continue tostep along the contacts 25 until no unbalance exists. During thestepping operation of wiper 17, relay 90 is held in by the action ofdiode 134 and capacitor 136 to permit wiper stepping to continue until abalanced condition is reached.

If wiper 17 reaches the end of its travel before a balanced conditionhas been reached, means (not shown) cause limit switch 140 in switchassembly 16 to move against contact 141 to pull in relay 64 through line142 and thus return wipers 17-21 to their home position to start arecycle of their movements in the decade direction. After a balancedcondition has been reached, that is, the potential between switch 56 andground being equal to the potential between the contact 25 engaged bywiper 17 and ground, module 96 or longer conducts and relay 108 isdeenergized to break the circuit to solenoid 132 with the consequentdeenergization of relay 90.

Deenergization of relay 90 causes the error sensing module 96 to beconnected to the units section of the control switch 11 and to thereference potential contacts 26 and further causes switch 122 of relay108 to be connected to a units solenoid 144 in switch assembly 16 tocause wipers 18-21 to close against the selected contacts 26-29. Theunits error potential from switch 58 in control switch 11 is connectedby line 146 through contact 92 (closed against switch blade 91) to lineleading to the module 96. The reference potential in the contact banks22 is picked up by the units position wiper 18 and is transmittedthrough line 148 to contact 102 (closed against switch blade 101) toline 103 connected to module 96. Since wiper 18 would not be closedagainst any one of the contacts 26 at the beginning of this switchingoperation, the unbalanced condition to start the stepping operation isprovided by the switch blade 150 closed against its contact 151. Theblade 150 is connected by line 153 to the unbalanced voltage line 47from the power supply. Contact 151 is connected by line 154 to contact102 (closed against switch blade 101) and thus to line 103 leading tothe error sensing module 96. As long as an electrical unbalance existsbetween wiper 18 or switch 150-151 and the switch 58 in the studentcontrol switch 11, the module 96 will energize relay 108 for closingswitch 122 in the manner previously. described. With switch 122 closedand switch blade 66 closed against contact 67, current will flow fromthe power supply through the line 48 through switch blade 66 and itscontact 67 to switch 122, and then through line 156 to switch blade 126closed against its contact 127. Said current then flows through line 158and interrupter contacts 160 in the switch assembly 16 for energizingthe units solenoid 144. Energization of the solenoid 144 causes means(not shown) to advance wipers 18-21 in a units direction inwardly intothe contact banks 22. The interrupter contacts 160 create a pulsation ofthe energization of the solenoid 144 to cause said wipers toautomatically step in this units direction. Such stepping will continuewith the wiper 18 moving along contacts 26 until no unbalance exists.

If wiper 18 reaches the end of its travel before a balanced condition isreached, means (not shown) cause limit switch 140 to close againstcontact 141 in switch assembly 16 to thus pull in relay 64 through line142 in the manner previously described and thus return wipers 17-21 tothe home position so that wiper 17 will again start to seek a balancedcondition in the manner previously described. After a balanced conditionhas been reached, that is, the potential between switch 58 and groundbeing equal to the potential between the contact 26 engaged by wiper 18and ground, relay 108 opens to break the circuit to the units solenoid144.

With the unit in its balanced condition, contacts 19-21 will be closedagainst the selected contacts 27-29, respec-,

tively, in contact banks 22. As shown in FIG. 2, the student controlunit 10 is provided with a switch 163 connected to headphones 12 andselectively closable against contacts 164, 165, and 166. Said contactsare connected by lines 167, 168, and 169 to wipers 19-21, respectively.Thus, the switch 163 permits the student to select which of the contacts19-21 will be connected back through the headphones for selecting thedesired lesson 23.

The embodiment of my invention illustrated in FIGS. 4-6 shows how myinvention can be employed with a dial type selector switch at thestudent location instead of the digital selector shown in FIG. 2. Inthis embodiment, the student control unit 10 comprises a dial selectorswitch 11' and headphones 12 connected to an adapter module 14' throughplug P and socket S Said module is connected through the plug and socketP and S to the power source 15 and through the plug and socket P and Sto the two-motion switch assembly 16 having the plurality of wipers17-21 selectively engageable with the banks of contacts 22, with thecontacts 25 and 26 in said banks f contacts engageable with wipers 17and 18 also being connected to the power source 15. As previouslydescribed, the contact banks 22 comprise one bank of ten contacts 25 inthe decade direction and one bank of ten contacts 26 in the unitdirection, with additional banks of unit contacts 27, 28, and 29. Aswith the previously described embodiment, each of the lessons 23 isconnected to ground, as at 24, and to one of the contacts 27, 28 or 29.

As shown in FIG. 5, the power supply 15, which may be the same powersupply shown in FIG. 2, but with some of its components not employed, isconnected to grourid at 32, with the contact banks 22 being connected tosaid ground through line 33. One side of the headphones 12 is alsoconnected by line 35 to ground 32. The opposite side of said headphonesis connected to the switch 163 selectively closable against contacts164, 165, and 166 connected by lines 167, 168, and 169 to wipers 19-21,respectively. Power supply 15 is also connected by line 37 to the bankof contacts 22 and to the module 14 by the DC power line 48, line 48supplying the necessary voltage to operate the various solenoids andrelays in the adapter module 14 and switch assembly 16. Since thisembodiment of the invention does not employ the error sensing module 96,it is, of course, not necessary for the power supply 15 to supply thevarious reference voltages to the contact banks 22.

As shown in FIG. 5, the control unit 10 comprises a switch having one ofits sides connected by the ground line 35 to ground 32 and its oppositeside connected by line 177 to dial switch 178. Said dial switch isconnected by line 180 to one side of a relay 182, the opposite side ofsaid relay being connected to line 48 leading from the power supply.Thus, with switch 175 open, relay 182 will be deenergized. Upon closingswitch 175, the circuit to relay 182 will be closed to thus energizesaid relay for moving contact blade 184 from its contact 185 to contact186 and moving switch blade 187 from its contact 188 to contact 189.With blade 184 closed against contact 186, the power from line 48 istransmitted through lines 190 and 192 and through diode 193 to contact195 and blade 196 in the switch assembly 16. Blade 196 is connected byline 198 back to one side of relay 200 in module 14, the opposite sideof said relay being connected by line 35 to ground 32. Energization ofrelay 200 causes switch blade 202 to move from its contact 203 tocontact 204 and switch blade 205 to move from its contact 206 to contact207.

Energization of relay 182 further causes power from line 48 to be fedthrough switch blade 184 and contact 186 to line 190 for transmissionthrough line 192 and diode 208 to one side of relay 210, the oppositeside of said relay being connected by line 35 to ground 32. Energizationof relay 210 causes switch blade 212 to move from its contact 213 tocontact 214.

When the student dials the first digit of the lesson number to beselected on dial switch 178, the train of pulses from said switchtransmitted to relay 182 and said relay will follow said train ofpulses, With relay 182 following the train of pulses, switch blade 187will open and close against contact 188 to transmit said pulses throughline 215 to switch blade 212 and contact 214. Contact 214 is connectedby line 217 to switch blade 205 closed against contact 207. Contact 207is connected by line 220 to one side of the decade solenoid 132, theopposite side of said solenoid being connected by line 224 to line 35leading to ground 32. The pulses transmitted to solenoid 132 cause it tobe energized and deenergized in response to said pulses to cause means(not shown) to advance wipers 1721 in a decade position in the contactbanks 18 in accordance with the number of pulses dialed. In suchadvancement, wiper 17 steps from one contact to another and wipers 1821step along the banks of contacts 2629 in a left-right direction.

When the wipers 17-21 move oif their home positions, blade 196 in switchassembly 16 will move from contact 195 to contact 225 thus breaking thepower supply circuit to relay 200. However, capacitor 226 wired acrossrelay 200 will hold said relay energized to retain blade 205 againstcontact 207 during the pulsing. Capacitor 226 is kept charged during thefirst train of pulses by switch blade 184 closing against contact 185 sothat power from line 48 is transmitted through blade 184 and contact 185to line 230 leading to blade 202 closed against contact 204 which isconnected to relay 200. As soon as the first train of pulses iscompleted, relay 200 will be deenergized, thus permitting switch blades202 and 205 to close against contacts 203 and 206. Relay 210 will beheld energized to keep blade 212 closed against contact 214 during thetrain of pulses by capacitor 227. Capacitor 227 is kept charged by blade184 pulsing closed against contact 186 so that power from line 48 istransmitted to said capacitor through lines 190 and 192 and diode 208.

When the second train of pulses is dialed on dial switch 178, saidpulses are again transmitted through line 180 to deenergize relay 182 inresponse to said pulses. As said relay is energized in response to thepulses dialed, blade 187 will open and close against contact 188 so thatsaid pulses are transmitted through line 215 to blade 212 and contact214 and thus to blade 205 through line 217, Because relay 200 isdeenergized during the second train of pulses as consequence of blade196 closing against contact 225 in the swiching assembly 16, blade 205will be retained closed against contact 206 during the second train ofpulses. The pulses transmitted to contact 206 during the second train ofpulses. The pulses transmitted to contact 206 are transmitted throughline 234 to the limit switch 140 in the switching assembly 16. Saidlimit switch is closed against contact 236 which is connected by line238 to one side of the units solenoid 144, the opposite side of saidsolenoid being connected by line 224 and 35 to ground. The pulsestransmitted to solenoid 144 cause it to be energized and deenergized inresponse to said pulses to cause means (not shown) to advance wipers1821 inwardly along contacts 2629 in response to the number of pulsesdialed. If said wipers should reach the end of their travel Withouthaving closed against the number of the contacts in the contact banks 22which was dialed, means (no shown) causes limit switch 140 to open fromcontact 236 and thereby prevent additional pulses from reaching solenoid144. As with the other embodiment of my invention, selection by thestudent of switch 163 will determine which of the wipers 19-21 will beinterconnected between the dialed lesson num'ber and headphones.

Relay 210 will remain energized during the second train of pulses byreason of blade 184 opening and closing against contact 186 to feedpower to capacitor 227. However, when student switch 175 is opened, thecircuit to relay 182 will also be opened causing said relay to bedeenergized. Deenergization of relay 182 causes switch blade 184 to moveagainst its contact 185 so that power from line 48 is prevented fromflowing to relay 210, and as soon as capacitor 227 discharges, saidrelay will also be deenergized so that switch blade 212 will moveagainst contact 213. Thus, with switch blades 187 and 212 closed againsttheir contacts 188 and 213, power from line 48 will be transmittedthrough said switch blades and contacts to line 242 leading to switchblades 74 and 75 in the switch assembly 16. The blades 74 and 75 areclosed against their contacts 72 and 73 which are connected by line 76to one side of the reset solenoid 78, the opposite side of said solenoidbeing connected to ground 32 through lines 224 and 35, This energiZesreset solenoid 78 to cause it by means (not shown) to return the wipers17-21 to home position. Thus, opening of student control switch causesthe wipers to be moved to their home position to reset the unit.

As has been described, the digital type student control shown in FIG. 2and the dial type student control shown in FIG. 5 can be employedinterchangeably in the system. Changing from one type of control toanother merely involves changing the adapter module 14 or 14' and itsconnections to its associated switching assembly 16 and the power supply15, as well as changing the connections from the power supply to thecontact banks 22. This can be simply and easily accomplished by pluggingin the proper module 14 or 14 into sockets S and S and plugging theproper control unit 10 or 10' into socket S For ease of description,each of the embodiments described herein has been described as employinga single student control unit connected to an individual module 14 or14', an individual switching assembly 16, an individual power supply 15,and an individual bank of contacts 22, with the lessons 23 beingconnected to the contact banks 22. In practice, however, a single set oflessons 23 can be connected to pluralities of the contact banks 22, anda single power source 15 is connected to pluralities of the studentcontrol units 10 and/or 10, contact banks, adapter modules 14 and/or 14,and switch assemblies 16. It is to be understood, of course, thatpluralities of both the control units 10 and 10' with their associatedmodules 14 and 14', switching assemblies 16, and contact banks 22 can beemployed in the same system with a common power supply 15 and common setof lessons being connected thereto.

While my invention has been described as being used in association witha two-motion switch, it is to be understood, of course, that it may beemployed with any type of conventional switch arrangement in which aplurality of messages can be selectively actuated.

I claim:

1. In a message retrieval system for supplying a plurality of audiomessages to a remotely controlled listening station, the combinationcomprising a first and a second set of contacts arranged in a bank, aplurality of message source means connected to said second set ofcontacts, a switch assembly having first and second wipers movabletogether to contact said first and second sets of contacts respectivelyand having relay means adapted to drive said wipers, audio receivingmeans coupled to said second wiper, a selector switch located at thelistening station, means for connecting a plurality of different voltagepotentials to said first set of contacts and to said selector switch,and module means responsive to the positioning of said selector switchto produce signals for actuating said relay means to step said wipersalong said sets of contacts until the voltage contacted by said firstwiper corresponds to the voltage selected on said selector switch,wherein said module means comprises a PNP and an NPN transistor havingtheir emitters connected together and their bases connected together andhaving their collectors connected to opposite potentials, the selectorswitch voltage being coupled to said bases and the first wiper voltagebeing coupled to said emitters, whereby transistor current flow, causedby a base to emitter voltage difference, actuates said relay means.

2. The invention as set forth in claim 1 in which said selector switchhas dual separately operable selecting contacts and said switch assemblycomprises a two motion switch having a third wiper for movement withsaid first and second wipers to contact said first set of contacts,Wiper switch means for alternately coupling said first and third Wipersto the bases of said transistors to cause said switch assembly to bedriven first in one direction to correspond to the positioning of one ofsaid selecting contacts and then in its second direction of motioncorresponding to the positioning of the other one of said selectingcontacts.

3. The invention as set forth in claim 1 in which said second set ofcontacts forms a plurality of banks of contacts, each bank having aseparate wiper engaged therewith and each contact having a separatemessage connected thereto, and further comprising a multiple positionswitch having a movable arm and at least as many contacts as there arebanks of contacts in said second set, said multiple position switchcontacts being connected respectively to said separate Wipers and saidmovable arm being connected to said audio receiver means.

4. The invention as set forth in claim 3 further comprising means toreset said wipers to an initial position with each adjustment of saidselector switch.

References Cited UNITED STATES PATENTS 1,237,208 8/1917 Keith. 1,555,95210/1925 Owen. 2,547,043 4/1951 Pouliart. 2,688,659 9/1954 Buchner.2,693,504 11/1954 Buchner. 1,812,169 6/1931 Powell. 2,328,,5 62 9/ 1943Lesavoy. 2,454,809 11/ 1948 Kruithof et al. 3,199,226 8/1965 JOSlOW.3,217,104 11/1965 Tabet.

KATHLEEN H. CLAFFY, Primary Examiner 20 C. JIRAUCH, Assistant ExaminerUS. Cl. X.R. 3535

